<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
.container {
     overflow: hidden;
 }
 .container > div {
     position: relative;
     float: left;
     height: 100px;
 }
 .main{
    overflow: hidden;
    margin: 0 200px;
    background-color: black;
    height: 100%;
 }
 .center {
     width: 100%;
     background-color: red;
 }
 .left {
     width: 200px;
     background-color: green;
     margin-left: -100%;
 }
 .right {
     width: 200px;
     background-color: blue;
     margin-left: -200px;
 }
</style>
<body>
    <div class="container">
        <!-- 优先渲染 -->
        <div class="center">
            <div class="main">
                center
            </div>
        </div>
        <div class="left">
            left
        </div>
        <div class="right">
            right
        </div>
    </div>
</body>
<script>
    a=0
    b=1
    if(a==0){
        if(b==1){
            console.log('1')
        }
        console.log('2')
        return ;
    }
</script>
</html>